On This Day . . .

Clouds Inside A Cave

December 27, 1966: Cave of Swallows Discovered

At least the first documented exploration of the cave by T.R Evans, Charles Borland and Randy Sterns. The Cave of Swallows is the largest known cave shaft in the world. It is so deep that clouds form inside it.

San Luis Potosi

The Cave, also called Cave of the Swallows, is an open air pit cave in the Municipality of Aquismón, San Luis Potosí, Mexico. The mouth is 49 m by 62 m (161 ft x 203 ft) wide. The floor widens to a room approximately 303 by 135 meters (994 ft by 442 ft).

The floor of the cave is a 333 meter (1092 ft) freefall drop from the lowest side of the opening, with a 370 meter (1,214 ft) drop from the highest side, making it the largest known cave shaft in the world, a skyscraper such as New York’s whole Chrysler Building could easily fit within it.

Despite its name, this natural refuge doesn’t host swallows, but rather white-collared swifts (apus apus) and the parrots Aratinga holochlora, known as green conures.

Apus

Green Conure

These birds do a morning ritual. At dawn, thousands fly in an orderly fashion to the coasts of Veracruz, more than a hundred kilometers away, in search of food. To exit the cave, the birds fly in circles, gradually flying upwards until they reach the surface. This exodus has become part of the tourist attraction.

The cave is a popular vertical caving destination. The high side of the mouth is covered with heavy foliage, so cavers most often fix their ropes on the low side, where bolts have been fixed into the rock and the area is clear of obstructions. Rappelling to the floor takes about twenty minutes, in which time abseil (descending) equipment and rope can heat up to hazardous levels. Cavers use water spray to cool their equipment.

Climbing back out may take from forty minutes to more than two hours. A person without a parachute would take almost ten seconds to freefall from the mouth to the floor. An average-sized hot air balloon has been navigated through the wide opening and landed on the floor below. Base jumping, or being extracted by rope is no longer allowed. Local villagers are focused on protecting the birds.